The OP is comparing two particular versions of each car, so I'm guessing the price difference isn't a concern. He is simply looking the membership who have experience of each to give their opinions as to what is best.

If a third row was important to him then maybe other SUVs would probably have been included, like the GL and Q7 among others. The fact he has narrowed it down to the X5 and Cayenne suggests that driving dynamics are very important and as such the Cayenne is the star here, no doubt.